Development of efficient luminescent materials in the aggregated state is important for various practical and theoretical applications such as organic light-emitting diodes (OLEDs), transistors, organic lasers, as well as fluorescent sensors or probes. However, traditional π-conjugated fluorophors are prone to aggregate with light emission quenching due to the formation of detrimental species such as excimers and/or exciplexes, which is a famous phenomenon known as aggregation-caused quenching (ACQ). Since 2001, our group has observed an opposite phenomenon termed "aggregation-induced emission" (AIE) and proposed the restriction of intramolecular rotation (RIR) as the main reason for the AIE effect. Guided by the RIR mechanism, I have launched a series of new programs directed...[ Read more ]

Development of efficient luminescent materials in the aggregated state is important for various practical and theoretical applications such as organic light-emitting diodes (OLEDs), transistors, organic lasers, as well as fluorescent sensors or probes. However, traditional π-conjugated fluorophors are prone to aggregate with light emission quenching due to the formation of detrimental species such as excimers and/or exciplexes, which is a famous phenomenon known as aggregation-caused quenching (ACQ). Since 2001, our group has observed an opposite phenomenon termed "aggregation-induced emission" (AIE) and proposed the restriction of intramolecular rotation (RIR) as the main reason for the AIE effect. Guided by the RIR mechanism, I have launched a series of new programs directed towards the development of new AIE materials and exploration of their OLED and biological applications.

In this work, a series of new AIE luminogens with emission colors covering from deep blue to near-infrared (NIR) region with high fluorescence quantum yields close to unity has been designed and synthesized. The high-tech applications of these efficient AIE emitters are investigated and the detailed results and discussions are summarized in Chapter 2-7.

Deep blue emission is crucial for full color displays and organic white lighting. The deep blue AIE emitters could be easily designed with a weakly conjugated AIEgen (triphenylethene) as the building block for molecular construction through a simple and successful molecular design strategy. Efficient non-doped deep blue OLEDs and white OLEDs fabricated from AIE luminogen (BTPE-PI) as deep blue emitter show good performances (Chapter 2).

The bifunctional materials are important for OLED development due to the simpler device fabrication, higher device lifetime and a lower production cost. Introduction of arylamines into AIE luminogens by the modulation of donor-acceptor (D-A) system are the new strategy to generate blue to red emitters with bifunctional properties of high hole transportation and strong solid-state light emission. Bilayer EL devices with green or red AIE luminogens as both hole-transporting and emitting materials show comparable or even better performances to those of devices with NPB as hole-transporting layer (Chapter 3-4).

The efficient red or far-red/near-lR AIE luminogens encapsulated with specific surface functional groups can be facilely formulated nanoparticles (alias "AIE dots"). The AIE dots show comparable photostability (under imaging conditions), brighter fluorescence, better fluorescence stability as well as ideal non-invasive long-term in vitro and/or in vivo cell tracing ability over commercial quatum dot(QD)-based cell tracing probes. More importantly, unlike QD-based probes, the organic fluorescent dots do not blink, and also do not contain heavy metal ions that could be potentially toxic when applied for living systems. These merits make the AIE dots promising alternatives to QDs in fluorescence imaging (Chapter 5-7).